The present invention relates to active suspension systems for vehicles, and in particular to such systems which include active roll control.
It can be a problem with active suspension control systems that whilst cornering of the vehicle and roll of the vehicle both produce lateral accelerations, the respective responses required from the suspension system are quite different. There is therefore a need for rapid and accurate measurement of true cornering acceleration thereby allowing the suspension control system to respond in the desired manner. Similarly, accurate determination of the amount of lateral acceleration due to cornering allows accurate determination of the amount of lateral acceleration due to other causes, for example xe2x80x98rock-rollxe2x80x99 which is a motion induced by roughness in the surface over which the vehicle is traveling and comprises rotation about a longitudinal axis of the vehicle, generally at a higher frequency than that of cornering-induced body roll. This in turn allows the correct control of the suspension to take account of the rough surface producing the rock-roll type motion.
It is known form U.S. Pat. No. 4,852,903 to provide an active suspension system in which a lateral accelerometer is used to measure lateral acceleration, and wheel height sensors are used to measure roughness in the road surface. The response of the system to measured lateral acceleration is modified of the wheel height sensors determine that the vehicle is traveling on a rough road because it is assumed that this is contributing a high frequency component to the lateral acceleration.
It is a problem with this system that separate systems are required for measuring lateral and vertical acceleration, and the effect of a rough road on measured lateral acceleration can only be very roughly estimated.
The present invention provides apparatus for measuring vehicle movement including a first accelerometer for measuring the lateral acceleration at least one point on the vehicle so that they measure different accelerations during roll movements of the vehicle, and control means arranged to measure lateral acceleration using the first accelerometer, to measure vehicle roll using the two accelerometers, and to measure vehicle cornering on the basis of the component of the lateral acceleration which is not due to vehicle roll.
The present invention further provides apparatus for measuring vehicle movement including roll measuring means for measuring roll movements of the vehicle, and also including lateral acceleration measuring means for measuring the lateral acceleration at least one point on the vehicle, and control means arranged to determine the amount of body roll which is not caused by cornering.
The present invention further provides a vehicle suspension system comprising apparatus according to the invention wherein the control means is arranged to control the roll stiffness of the vehicle, wherein the control means is arranged to alter the suspension characteristics, for example by reducing roll stiffness, in response to the detection of vehicle roll movements which are not caused by cornering.